1. Field of the Invention
This invention relates to carbonaceous materials and, more particularly, to carbonaceous materials coated with molybdenum carbide and metal composites of the same.
2. The Prior Art
Carbonaceous materials exhibit valuable characteristics depending upon the particular type of carbonaceous material. These carbonaceous materials include all forms of carbon such as diamond, graphite, amorphous forms of carbon such as lampblack, and even carbon-rich surfaces. Each of these forms of carbon are generally available in particulate shapes while graphite can be found in a variety of forms including fibers, both continuous and discontinuous, as well as flakes and particulates. The carbon-rich surfaces can, in turn, be prepared from a substrate in the form of fibers and particulates as well as any predetermined shape having thereon the carbon-rich surface.
The physical and chemical characteristics of carbon depends upon the atomic structure of each. For example, in diamond the atoms are arranged in such a way that each carbon atom is at the center of a regular tetrahedron and is bonded to four other carbon atoms, each of which lies at the corners of the tetrahedron. Diamond thus is formed with its carbon atoms bonded together as a series of interlacing hexagons with each carbon atom covalently linked to four others. This accounts for diamond being well known for its extreme hardness. On the other hand, the graphite form of carbon consists of sheets or planes of covalently linked carbon atoms, but these sheets are almost too far apart for them to have real chemical bonds between the carbon atoms in different planes. This structure accounts for the readiness with which graphite can be cleaved along these planes as well as its softness and lubricating power.
Charcoal and amorphous forms of carbon in general are found to possess a graphite-like structure but the planes are much smaller and arranged in an irregular manner. This accounts for the greater reactivity but also lends support to the view that amorphous carbon is not a distinct allotropic form.
Graphite fibers could also be considered to be another form of carbon due to their unique properties, primary of which is its high modulus or stiffness as well as elasticity and strength. Certain graphite fibers also have high thermal conductivity which makes these graphite fibers uniquely qualified for uses that can benefit from these features. Another advantage is that graphite fibers are relatively light weight which means that when incorporated into a composite they will significantly reduce the specific gravity of that composite while at the same time contributing to the overall strength and thermal conductivity of the composite. Graphite fiber also has a very low coefficient of thermal expansion which means that a composite having graphite fibers therein should have a correspondingly low coefficient of thermal expansion.
Probably the greatest obstacle to the use of these carbonaceous materials in any of their various forms in matrices, particularly metal matrices, is their rather high degree of reactivity with oxygen and most molten metals especially at the melting temperatures of these metals. Another significant problem is that these carbonaceous materials are difficult to wet with some molten metals unless special wetting agents are used. However, many metals readily react with the graphite fibers and thereby "wet" the graphite fibers albeit at the expense of the graphite fibers since this reaction significantly degrades the graphite fibers. Therefore, a number of patents have been granted for inventions involving the production of graphite fiber-metal composites wherein various coatings have been applied to the graphite fibers.
However, none of these references either disclose or suggest the novel technique of protecting carbonaceous materials by coating them with molybdenum carbide. We have discovered that we can produce a protective coating of molybdenum carbide on carbonaceous materials to both protect the carbonaceous materials against attack by the molten metals while simultaneously providing the surface of the carbonaceous materials with a wetting action for the thorough wetting of the carbonaceous materials with molten metal. The carbonaceous materials include all forms of carbon such as diamond; graphite fibers, both continuous and discontinuous; graphite particulate, lampblack, and even carbon-rich surfaces such as a carbon-coated silicon carbide. These molybdenum carbide coated carbonaceous materials can then be incorporated into selected metal matrices. These metals include copper, aluminum, magnesium, iron, nickel, cobalt, titanium, silver, gold, platinum, rhodium, tin, zinc, and alloys of these metals. Such a novel invention is disclosed and claimed herein.